With an increase in the recording density of magnetic disks, the distance between the magnetic disk serving as a recording medium and the head for use in recording of information or playback has become almost nil close to contact therebetween. The magnetic disk is provided over the surface thereof with a carbon protective film or lubricant film for the purpose of diminishing abrasion due to the contact or sliding of the head thereon or preventing contamination of the disk surface.
The carbon protective film is produced generally by the sputtering process or CVD process. The disk surface is protected with the two films, i.e., the carbon protective film and the lubricant film thereover.
The lubricants generally in use are fluoropolyethers having functional groups. Examples of functional groups are hydroxyl, amino and cyclophosphazene groups. Examples of these lubricants include Fomblin ZTETRAOL manufactured by Solvay Solexis Inc. and having hydroxyl at the terminals of the molecule and PHOSFAROL A20H manufactured by MORESCO Corporation, and having hydroxyl at one terminal of the molecule and a cyclophosphazene group at the other terminal thereof. Further proposed are lubricants having hydroxyl at a molecular terminal and also in the molecular chain (Patent Literature 1).
Fomblin ZTETRAOL exhibits good adsorption to the disk due to the presence of hydroxyl positioned at the opposite terminals of the molecule and is capable of retaining the film of lubricant without permitting spattering even if the disk is rotated at a high speed. Described in Patent Literature 1 is the influence of the film thickness of the lubricant on the spacing between the head and the disk. The spacing can be effectively diminished by reducing the mono-layer thickness of the lubricant. This leads to the proposal that lubricants can be reduced in mono-layer thickness when having hydroxyl at a molecular terminal and also in the molecular chain. This technique makes it possible to diminish the lubricant in the mono-layer thickness.
However, such fluoropolyether compounds are low in durability against Lewis acids and react with Al2O3 in component members of the head to cut the main chain (see, for example, Nonpatent Literature 1). If this cutting proceeds, the compound becomes lower in molecular weight and eventually evaporates off and disappears from the disk surface, failing to maintain the lubricant film in the case of systems wherein the head moves in contact with or slides on the disk.
Lubricants have been proposed which exhibit improved characteristics to adsorb to the protective layer over the lubricant and have high durability against the environment wherein the magnetic head is levitated at a low level for a rapidly increasing ever-higher recording density. Heretofore proposed as such lubricants are those containing a compound wherein perfluoropolyether groups having a perfluoropolyether main chain and hydroxyl at a terminal are connected to each other by a connecting group having hydroxyl in the structure (Patent Literature 2). Nevertheless, Patent Literature 2 discloses no substantial examples but merely states that the exemplified compound is reacted under a base condition to thereby merely produce the exemplified lubricant compound, is mute about the particular diepoxy compound used and no where is there disclosed any data, such as NMR, for specifying the product.    Patent Literature 1: JP2006-70173A    Patent Literature 2: JP2010-86598A    Nonpatent Literature 1: Macromolecules, 1992, vol. 25, p6791-6799    Nonpatent Literature 2: Journal of Tribology, October 2004, vol. 126, p751
An object of the present invention is to provide a stabilized compound which remains free of decomposition even if brought into contact with the head and is capable of diminishing the spacing between the head and the disk, lubricants comprising the compound, and magnetic disks.